The present invention relates to a metal-pipe bonded body and a pipe expansion method of metal-pipe bonded body, and to more particularly relates to an expandable metal-pipe bonded body and a pipe expansion method of metal-pipe bonded body that are favorable for plant piping and line pipes used in the chemical industry, petrochemical industry, etc., and for casing tubes, production tubes, coiled tubes, and other oil well pipes used in oil wells.
In addition to this, the present invention also relates to a metal pipe bonded body inspection method, and more particularly relates to a metal pipe bonded body inspection method that is favorable as a nondestructive inspection method for a metal pipe bonded body having a inclined part at the bonded interface and is liquid phase diffusion bonded.
Since in the fields of chemical industry, petrochemical industry, etc., long-size metal pipes have been conventionally used for obtaining the targeted products by use of chemical reactions under various environments and for transporting the chemical reaction raw materials, intermediate products, targeted products, and other corrosive fluids over a long distance.
Though seamless steel pipes, which are excellent in corrosion resistance, are generally used as metal pipes that are exposed to corrosive environments, industrially mass-produced seamless steel pipes are 10 to 15 m in length and the upper limit for production is approximately 100 m. Thus in such cases, bonded bodies (referred to hereinafter as xe2x80x9cmetal pipe bonded bodiesxe2x80x9d), with which a plurality of seamless steel pipes of 10 to 15 m length are joined, are used.
Conventional methods for joining metal pipes include the screw connecting method (mechanical coupling method), welding methods (orbital welding method), friction welding method, diffusion bonding method, etc. Among these, the diffusion bonding method provides the advantages that a joint, which is high in air-tightness and is of a bonding strength that is equivalent to the base material strength, can be obtained and the working time is short in comparison to the welding method. The diffusion bonding method is therefore anticipated for application as a method for joining oil well pipes, line pipes, etc.
Also, though a metal pipe bonded body is generally used as it is in the joined condition, depending on the application, the process of expanding the inner diameter of the metal pipe bonded body (this process shall be referred to hereinafter as xe2x80x9cpipe expansionxe2x80x9d) is carried out after the joining process in some cases. For example, recently in the field of oil well pipes, a method of performing pipe expansion after the burying of a metal pipe bonded body underground has been proposed for reducing the drilling cost of oil wells.
For example, a method of burying a casing, made of malleable material, in a bore hole drilled into the ground and expanding a hydraulic expanding tool inside the interior of the casing to expand the casing in the radial direction with respect to the bore hole wall has been disclosed in Japanese Patent Publication No. 507610 of 1995.
Also, International Patent Publication No. WO 98/00626, based on the Patent Cooperation Treaty, discloses a method of inserting a steel pipe, which is made of a malleable type of steel that undergoes strain hardening without undergoing necking or ductile breaking, inside a gallery or a previously buried casing, and pipe expanding the casing using a mandrel, made of nonmetallic material and having a tapered surface.
In applications of pipe expansion of a metal pipe bonded body to oil well pipes, the rate of expansion of the inner diameter before and after pipe expansion (shall be referred to hereinafter as the xe2x80x9cpipe expansion ratexe2x80x9d) must be at least 5% and is more preferably 20% or more for reducing the drilling costs of oil wells. On the other hand, the diffusion bonding method is, as has been mentioned above, a joining method that enables the production of high-quality metal pipe bonded bodies at high efficiency. Significant reductions in oil well drilling costs can thus be anticipated by combining the diffusion bonding method with pipe expansion and applying this to oil well pipes.
However, generally in the diffusion bonding of metal pipes, butt joining is performed upon forming the bonded interface by processing the end faces of the metal pipes to be perpendicular to the axial direction. Thus when pipe expansion is performed on such a metal pipe bonded body as it is, the shearing force that acts on the bonded interface during pipe expansion increases in accompaniment with the increase of the pipe expansion rate and this can lead to the formation of cracks at the bonded interface.
Conventionally, as a bonding method for a plurality of metal pipes that constitute a metal pipe bonded body, a liquid phase diffusion bonding method is known. Due to being lower in heat deformation than the welding method and enabling a joint of the same quality as the base material to be obtained in a short time, the liquid phase diffusion bonding method is used as the method for joining such metal pipes as plant piping, line pipes, oil well pipes, etc. However, the quality of a bonded body made by the liquid phase diffusion bonding method depends sensitively on the unavoidable variations of the bonding conditions, the expertise of the worker, etc. and flaws can occur at the bonded interface. Thus when metal pipes are joined by the liquid phase diffusion bonding method, the existence of flaws at the bonded interface must be inspected in a nondestructive manner in order to assure the quality of the metal pipe bonded body that is obtained.
The X-ray transmission test method or the ultrasonic flaw detection test method, etc. is generally used as a nondestructive inspection method for a bonded body. Among these, the X-ray transmission test method is good for the inspection of three-dimensional flaws, such as blow holes, etc. Meanwhile, the ultrasonic flaw detection test method is good for the inspection of planar flaws, such as cracks, etc. In the case of the liquid phase diffusion bonding method, since the flaws that occur at the bonded interface are normally planar flaws, such as cracks, bonding faults, etc., the ultrasonic flaw detection method is used for inspection of a metal pipe bonded body made by liquid phase diffusion bonding.
Also, generally when metal pipes are liquid phase diffusion bonded, the end parts of the metal pipes are processed to be perpendicular to the axial direction and butt joining is performed. Thus in the detection of the existence of a flaw at the bonded interface, the oblique flaw detection method is generally employed in which the ultrasonic wave is made incident obliquely on the bonded interface and the existence of a flaw is judged from the magnitude of the reflected wave.
However, the conventional oblique flaw detection method is limited in terms of high-precision quantitative inspection of the magnitudes, positions, and shapes of the flaws that occur at the bonded interface.
Also, the quality of a metal pipe bonded body is not only affected by the poor fusing that occurs at the bonded interface but is also affected by the offset that is formed at the end part of the bonded interface, the crystalline structure in the vicinity of the joined parts, etc. Also, molten insert material may leak out from the bonded interface and since the resulting solidified parts are brittle, they tend to be starting points for the concentration of stress. Therefore such solidified parts must also be inspected in a nondestructive manner in order to assure the quality of the metal pipe bonded body.
It is an object that this invention attempts to achieve is to provide a metal-pipe bonded body, with which the possibility of crack formation at the bonded interface is low even when pipe expansion of a high pipe expansion rate is carried out. It is another object of the present invention to provide a pipe expansion method of metal-pipe bonded body, which enables pipe expansion of a high pipe expansion rate to be performed without causing cracks to form at the bonded interface.
The object can be achieved by a metal-pipe bonded body, according to the present invention, having a plurality of metal pipes which are diffusion bonded via a bonded interface formed at the end parts thereof. In the metal-pipe bonded body, at least part of the bonded interface is inclined with respect to the radial direction of the metal pipes.
Since with the metal-pipe bonded body of this invention, at least part of the diffusion bonded bonded interface is inclined with respect to the radial direction of the metal pipes, the shearing force that is generated at the bonded interface in the process of pipe expansion can be alleviated by moving a pipe expanding tool from one metal pipe, with which the inclined part of the bonded interface is formed to have a protruding shape, towards another metal pipe, with which the inclined part of the bonded interface is formed to have a recessed shape. Pipe expansion of the metal pipe bonded body can thus be performed without the formation of cracks at the bonded interface.
It is a further object of the present invention to provide a metal pipe bonded body inspection method by which flaws, which have occurred at the bonded interface of a metal pipe bonded body, can be detected at high precision. It is another object of the present invention to provide a metal pipe bonded body inspection method by which the magnitude of the offset that has formed at the end part of the bonded interface, the appropriateness of the crystalline structure in the vicinity of the bonded interface, and the existence of insert material that has leaked out and solidified at the end part of the bonded interface can be inspected.
In order to achieve the above objects, this invention provides in a metal pipe bonded body inspection method for inspecting, by the ultrasonic flaw detection method, a metal pipe bonded body at which a plurality of metal pipes are joined by liquid phase diffusion bonding, a metal pipe bonded body inspection method being characterized in that the bonded interface of the metal pipe bonded body has a inclined part and in having a first flaw detection process, in which an ultrasonic wave is made incident perpendicularly on the inclined part and the reflection echo that is reflected from the inclined part is detected.
Since the method of making an ultrasonic wave perpendicularly incident on the inclined part and detecting the reflection echo is employed in the metal pipe bonded body inspection method of this invention, the maximum sensitivity can be obtained. Also, by focusing the ultrasonic wave and scanning in the circumferential direction or longitudinal direction, the flaw information on the inclined part can be obtained as 2-dimensional information, and the magnitudes, positions, shapes, etc. of flaws can be obtained from this flaw information.
Also in the case where the bonded interface has a perpendicular part, the inspection method preferably has furthermore a second flaw detection process, in which an ultrasonic wave is made obliquely incident on the perpendicular part and the reflection echo that is reflected from the perpendicular part is detected. The existence of flaws at the perpendicular parts of the bonded interface may thereby be inspected.
The inspection method may also have furthermore a first pipe thickness measurement process, in which an ultrasonic wave is made perpendicularly incident on one of the metal pipes that are disposed adjacent each other across the bonded interface and the pipe thickness of the one of the metal pipes is measured from the difference in the arrival times of the surface echo and the bottom face echo, a second pipe thickness measurement process, in which an ultrasonic wave is made perpendicularly incident on the other of the metal pipes that are disposed adjacent each other across the bonded interface and the pipe thickness of the other of the metal pipes is measured from the difference in the arrival times of the surface echo and the bottom face echo, a surface offset measurement process, in which the surface offset between the one of the metal pipes and the other of the metal pipes is measured, and an inner face offset calculation process, in which the inner face offset between the one of the metal pipes and the other of the metal pipes is determined from the pipe thickness and the surface offset of the one of the metal pipes and the other of the metal pipes. The inner face offset of the metal pipe bonded body can thereby be measured in a non-destructive manner.
Also, the inspection method may furthermore have a backward scattering intensity measurement process, in which an ultrasonic wave is transmitted in the direction of the interior of the metal pipe at the vicinity of the bonded interface and the backward scattering intensity is measured, and a crystal grain diameter calculation process, in which a previously determined correlation between the crystal grain diameter of the metal pipe and the backward scattering intensity is used to determine the size of the crystal grain from the magnitude of the backward scattering intensity that was measured in the backward scattering intensity measurement process. The crystalline structure in the vicinity of the bonded body can thereby be judged.
The inspection method may furthermore have a solidified phase detection process, in which an ultrasonic wave is made obliquely incident towards the inner face end part of the metal pipe bonded body and the position of the reflection echo that is reflected from the inner face of the metal pipe bonded body is measured. The existence of a solidified phase at the inner face end part can thereby be inspected in a non-destructive manner.